Answer :
[tex]3.5(c-8)+c=12.5\\\\3.5 c-28 +c=12.5\\\\4.5c=12.5+28\\\\4.5c=40.5\ \ / *10\\\\45c=405\ \ / :45\\\\c=\frac{405}{45}\\\\c= 9[/tex]
distribute 3.5 to c - 8. 3.5c - 28. now add the extra one c. 4.5c - 28. now do the other stuff, starting with changing minus to a plus negative, so 3.5c + -28. now add 28 to 28 and 12.5 to get 30.5. Now divide 3.5 by 30.5. it should be 8.71 (If i am correct...)